1. Field of the Invention
The present invention relates to an automated skip checker device for sewing machine which is provided to distinguish whether or not a slack appears on a sewing thread to detect a skip of stitch or a disconnection of an upper thread in operation.
2. Description of Prior Art
In a sewing machine, an upper thread entangles with a lower thread to form consecutive stitches on a cloth material by a combination of a reciprocal movement of a sewing needle and a rotary movement of a hook (looper), as the sewing needle repetitively perforates the cloth material. The consecutive stitches formed on the cloth material are usually at regular intervals, however, the skip of stitch may arise in which one or several stitches are not formed to render a series of stitches uneven while operating the sewing machine.
One of the causes of the skip of stitch is presumably due to an uneven thickness of the cloth or an unequal twisting degree of the sewing thread.
Other causes may be an inappropriate sewing needle and an improper set gauge of the hook (looper), or an incoordinated timing between the reciprocal movement of the sewing needle and the rotary movement of the hook (looper).
When the skip of stitch arises, it becomes necessary to interrupt the sewing operation and mend the sewing machine in a way depending on the causes of the skip of stitch.
Japanese Laid-open Patent Application No. 08-276088 discloses a detector device for detecting a skip of stitch which senses a frictional noise by means of a sound sensor when a sewing thread touches and slides along a thread guide.
More specifically, the sound sensor compares the frictional noise this time to the frictional noise last time in terms of its consecutive duration per a stitch of the sewing needle, in order to calculate a displacement difference of the sewing thread based on the duration difference of the frictional noise.
On the other hand, a rotary sensor detects a revolution of the sewing machine to calculate a displacement difference of the sewing thread based on the difference between the revolution this time and the revolution last time per a stitch of the sewing needle.
The rotary sensor further compares the former displacement difference of the sewing thread with the latter displacement difference of the sewing thread.
With the result that the displacement differences of the sewing thread are compared to distinguish whether or not the skip of stitch develops, it becomes possible to unerringly detect the skip of stitch even when the sewing thread varies levels of the frictional noise unevenly per a stitch of the sewing needle.
Japanese Laid-open Patent Application No. 50-54457 discloses a method of detecting a skip of stitch and disconnection of a sewing thread in a sewing machine. The detecting method is based on the fact that a hook (looper) fails to catch an upper loop of the sewing thread when the skip of stitch appears, and develops a slack on the sewing thread, a length of which corresponds to a dimensional amount that an upper thread travels around the hook (looper).
In this instance, a strain gauge is used to confirm a tension of the upper thread portion located between a thread take-up lever and the sewing needle upon distinguishing whether or not the skip of stitch appears. More particularly, a guide ring is provided, through which the upper thread passes to transmit a sliding pressure against the guide ring by means of the strain gauge, so as to detect the skip of stitch based on a predetermined amount of the sliding pressure subjected to the strain gauge.
However, the detector device of the former Japanese Laid-open Patent Application No. 08-276088 is structurally complicated so that it may become costly. Upon comparing the displacement difference of the sewing thread based on the difference of the revolution with the respective difference based on the duration difference of the frictional noise, it may arise a situation to change the comparing requirements depending on the sewing condition. Depending on the types of the cloth material, it may arise an occasion to change the predetermined amount of the value needed to distinguish whether or not the skip of stitch appears, thus making its distinction accuracy unstable.
In the detecting method of the latter Japanese Laid-open Patent Application No. 50-54457, the sewing thread has a tendency to often change the sliding pressure against the guide ring while operating the sewing machine, so that the strain gauge may fail to correspond the predetermined amount of strain to the skip of stitch, thus making its distinction accuracy unstable in the same manner as mentioned above.
Therefore, the present invention has been made with the above drawbacks in mind, it is a main object of the invention to provide an automated skip checker device for a sewing machine which is capable of detecting a skip of stitch cost-effectively with a simplified structure, and improving an accuracy of detecting the skip of stitch and a disconnection of the sewing thread, thereby ameliorating a sewing efficiency conducive to a mass production.